Interpretive Summary: Crimson clover is an annual forage that is grown in regions with Mediterranean-like climates for hay and grazing, and in the southeastern USA for overseeding with cool-season annual grasses in warm-season perennial grass pastures. The crimson clover cultivar Dixie has historically accounted for a major portion of the USA production as well as for international trade with Europe. However, under recently adopted rules for seed commerce in European Economic Community member countries, the importation of noncertified Dixie seed has slowly fallen since 1991 because it is not a certified cultivar and is not on the list of cultivars that can be imported. With the decline in Dixie exports, there has been a concurrent increase in the amount of seed production of certified Europe cultivars to more than 25% of the present USA market. Little is known about the genetic background of most crimson clover cultivars and whether newer cultivars are utilizing all available genetic diversity found in plant germplasm collections. This research found two major genetic groups of crimson clover cultivars exist as well as a group of more genetically diverse sources. Most of the existing cultivars have been selected from previously released cultivars and do not utilize unique genetic sources found in the National Plant Germplasm System collection. Because of the broad geographic range for crimson clover and its limited representation in available collections, other accessions should be acquired and evaluated to increase the genetic base of the present collection. This research will help crimson clover breeders identify new sources of genetic diversity that can be incorporated into their cultivars.

Technical Abstract:
There are few morphological traits that distinguish genotypes of crimson clover (Trifolium incarnatum L.). Little is known about the relatedness of present cultivars & the amount of genetic diversity that is available in the USDA-ARS National Plant Germplasm System (NPGS) for further cultivar development. The purpose for this research is to classify & determine differences among NPGS accessions & other crimson clover cultivars & identify accessions that may be potential sources of unique genes that can be utilized to develop new cultivars. Leaf samples from 36 accessions & cultivars obtained from the NPGS & other sources were examined by the polymerase chain reaction using 21 random amplified polymorphic DNA (RAPD) markers. General observations were made for inflorescence color & relative flowering time. Using cluster analysis, the accessions were classified into 2 major groups with the 2nd divided into 2 subgroups. A stepwise discriminant analysis based on the cluster analysis groupings correctly placed 94% of the accessions using 6 RAPD markers. The resulting 3 interpretive groups were distinguished by accessions that displayed nonred flower color & early- & late-flowering time. Improved cultivars have been primarily selected from previously released cultivars & tracing cultivar pedigrees with RAPD markers support their genetic similarity. None of the cultivars examined utilized genetic materials similar to those found in the most diverse interpretive group. Because of the broad geographic range for crimson clover & its limited representation in the NPGS collection, other accessions should be acquired & evaluated to increase the genetic base of the present collection.